1. Field of the Invention.
The present invention relates to holographic lenses and more particularly to a laser system which uses a holographic bifocal lens element.
2. Description of the Prior Art.
Laser systems are being utilized in ever-increasing applications to send a laser beam out and measure (in some desired manner) the retroreflected signal off some target. Examples of such applications are in the fields of laser scanners and laser range finders.
In many applications the optical system of a laser system must perform several distinct functions for efficient laser system operation. These functions include laser beam divergence/collimation/focusing, filtering background noise from the reflected signal light, and collection light focusing on a detector. Typically, these functions are performed by combinations of cold mirrors, lenses, and a colored plastic filter (or dyed color lens).
An optical system which includes a combination of cold mirrors, lenses and a colored plastic filter (or dyed color lens) can present a substantially wide bandwidth of about 1500 angstroms to light reflected from a target. Such a wide bandwidth also passes too much external overhead light (in the form of noise) through the optical system to the detector, thereby degrading the performance of the laser system.
The background art known to applicant at the time of the filing of this application is as follows:
U.S. Pat. No. 3,578,838, Multiple Hologram Recording and Read Out System, by J. N. Hallock;
U.S. Pat. No. 3,675,990, Reflective-Type Narrow Bank Filter, by H. W. Kogelnik et al.;
U.S. Pat. No. 3,807,829, Extended-Field Holographic Lens Arrays, by D. H. Close;
U.S. Pat. No. 4,245,882, Doubly Modulated On-Axis Thick Hologram Optical Element, by B. J. Chang;
U.S. Pat. No. 4,421,379, Multiple Holographic Lens, by A. Grumet et al.; and
U.S. Pat. No. 4,333,006, Multifocal Holographic Scanning System, by B. A. Gorin et al.
None of the above-cited prior art patents teaches or suggests a laser system which utilizes a single holographic bifocal lens element to perform all of the functions typically performed by an exemplary combination comprised of a cold mirror, lenses (a bifocal lens) and a color filter (or color lens).